In a unique effort to address the city's storm-water runoff problem, improve streets, benefit the community, and create jobs, the Philadelphia Water Department (PWD) has opted for green infrastructure solutions rather than simply digging new tunnels and storage tanks to hold runoff.

The city is relying on a combination of solutions including green roofs, porous paving, storm-water planters, rain gardens, and, of course, the coveted rain barrels. Crockett had hoped to encourage Philadelphia's residents to take a role in keeping their water clean, little expecting the program would be so popular that people would impersonate others to get their rain barrels.

In April, the U.S. Environmental Protection Agency (EPA) and the City of Philadelphia signed an agreement that will result in a $400,000 investment in Philadelphia's Green City Clean Waters program. This is in addition to the PWD's commitment of $1.2 billion (in today's dollars) drawn from water and sewer billing for green infrastructure over 25 years, which had been announced at the launch of Green City Clean Waters in 2010. That plan was widely hailed as an ambitious use of environmentally friendly solutions and helped the city rank first in the Natural Resources Defense Council's November 2011 report on green infrastructure.

Shawn M. Garvin, EPA regional administrator for the area encompassing Philadelphia, notes that the Green City Clean Waters program represents a shift in focus. "We spent a lot of time trying to clean water after it's polluted," says Garvin. "Now we're focusing on how to keep water from coming into contact with pollution in the first place. The likelihood is that this will be significantly more cost-effective than gray infrastructure."

The Schuylkill and Delaware rivers come together at Philadelphia, providing the city with its drinking water as well as popular and attractive waterfronts. As in many other U.S. cities, when bad weather overwhelms the storm-sewer system, the rivers become receptacles for untreated sewage and rainwater that picks up garbage, oil, and chemicals from parking lots and streets.

This is the result of what's referred to as a "combined sewer system," which brings together in the same pipes storm water from streets, businesses, and homes, as well as residential and commercial sewage. With tunnels that make up 60 percent of Philadelphia's sewer system, the combined sewer system serves more than three-quarters of Philadelphians, and covers 64 square miles. When these systems get hit by more water than they can carry to water treatment, the excess is released into the Schuylkill, Delaware, and other waterways at 164 combined sewer outflow (CSO) points, events that can happen up to 85 times a year.

Although these CSOs are sited downstream from drinking water intakes, the pollution can affect wildlife, fishing, and swimming. Within Philadelphia, as Crockett notes, the PWD's waterways restoration unit "pulls tons and tons of trash out of the streams every year."

The Green City Clean Waters program requires that green infrastructure be capable of keeping one inch of rainwater out of the storm-water system in a 24-hour period. Crockett explains that this will capture all of the water from 80 percent of the storms Philadelphia experiences.

This is no small amount of water: One acre of land in the city will receive approximately 1 million gallons of rainfall annually. In fact, the city already requires the capture of 1.5 inches for municipal projects.

Philadelphia's history of water-related invention extends back at least to Ben Franklin's swim fins and glass armonica, but the city is less well known for an invention that will soon cover a sizable portion of it—permeable paving. Developed at the city's Franklin Institute in 1977, permeable (also known as "porous" or "pervious") paving provides a surface tough enough to bear traffic while allowing water to seep through its matrix and into the soil, eliminating surface pooling.

An integral part of Philadelphia's green streets plan, permeable paving will replace 15 square miles of impervious paving within the city's CSO area in a little over 20 years. As Crockett notes, that's the equivalent of more than a thousand city blocks.

The city is also testing a variety of designs for other street elements—including 20 different types of tree trenches. Above ground, these look no different from street tree plantings elsewhere, but below the paving the structure is engineered to hold water to nourish the trees and allow some to enter the ground beneath.

When it's impractical to store water in the ground, green street engineers store it in the air. Flow-through planters take runoff from rooftop gutters and hold it in planter boxes until it returns to the atmosphere via "evapotranspiration" from leaves. Rain gardens set in low-lying areas where runoff can pool use both evapotranspiration and groundwater infiltration to store water.

As for the rain barrels, although they can hold only a small amount of water and must be emptied between storms, they are free on a one-barrel-per-household basis to Philadelphia residents who attend the PWD's educational workshop on installation and use. Since rain-barrel water can be used for gardening, watering lawns, or washing down patios and driveways, the tap water conserved could help lower water bills, perhaps explaining the degree of interest in them. Crockett, however, argues that residents genuinely want to help, and notes that Philadelphians also clamored for curbside recycling bins upon their introduction.

Progress to Date

So far, the city has completed 35 green street blocks, and by the end of the year expects to have boosted that total to 215. The PWD has removed 10,000 square feet of impervious paving. Sixteen green school projects have been completed and private businesses are now engaged in approximately 300 greening projects. The city also has an incentive program for storm-water billing that grants close to a 100 percent credit for green retrofits.

Of particular interest is the demonstration project at George W. Nebinger School in South Philadelphia. The schools' rain gardens, porous play surfaces, and other green features will serve as teaching tools in an environmental curriculum emphasizing the role of water.

"Students are our environmental stewards," says Garvin. "They are our best messengers at home and in the community. Partnering with Nebinger and the students and putting practices on the ground we're getting many bangs for our buck."

Adding salience to the effort is a study showing that green infrastructure may also provide significant health and social benefits. "The green infrastructure program is not just a 25-year program but a 50-to-100-year program in which the people who are underserved and underemployed will have job opportunities in their communities," says Crockett. "And people who work in their communities tend to invest in their communities."